The present invention relates to devices for protecting the members of an aircraft crew, and in particular the pilots of combat aeroplanes, against the effect of the high accelerations encountered during a mission, in particular ones caused by tight turns.
Current protective devices include a suit or at least a pair of trousers, which is equipped with pockets and control means which supply the pockets with compressed gas when the positive load factor (acceleration in the direction of the lower body) exceeds a specific threshold.
It is desirable for the response time of the device to be short, in order to ensure satisfactory protection. A variety of arrangements have been adopted for this purpose, in particular preinflation of the pockets at altitude (FR 2 395 890) and above all the use of a control law which, in the pockets of a pair of trousers, establishes an overpressure level of a specific value as soon as a predetermined positive load factor is exceeded, and which then increases the overpressure substantially linearly starting from a virtual origin corresponding to a negative load factor (EP-A-0136223 or U.S. Pat. No. 4,546,491); this law is, for example, the one schematically represented by dashes in FIG. 1.
It has now been found that the tolerance to positive load factors is temporarily reduced after exposure to a negative load factor. This reduction could explain accidents encountered in combat, training and aerobatic aircraft.
The degradation in the resistance to positive load factors Gz may reach several times the standardized value g.sub.n of the acceleration due to gravity following a few seconds of exposure to a zero acceleration or to a negative load factor (which may be as much as -3 g.sub.n in modern fighter aircraft). This degradation disappears after a few tenths of seconds, which are needed for re-establishing normal cardiovascular functions.
One might assume that the problem can be obviated by using a variation law for the pressure in the pockets which takes account of the worst case conditions. This solution entails a high degree of consumption of the inflation gas. It is a source of discomfort and fatigue for the individual wearing the trousers, the pockets of which will be inflated much more often and to a greater extent than is in general necessary.